Pneumatic percussion tool with slide valve control gear



oct. 14, 1941. A, HERZBRUCH '2,259,379

' PNEUMATIC PERCUSSION TOOL WITH SLIDE VALVE CONTROL lGEAR Oct. 14,1941. A. HERzBRuCH 2,259,379

PNEUMATIC PERCUSSION TOOL WITH SLIDE VALVE CONTROL GEAR Filed Aug. l1,1939 2 Shets-Sheet 2 Patented Oct. 14, 1941 .y PNEUMATIC PERCUSSIONTooLfWIrrr i f l SLIDEVALVE CONTROL f f August g 'H erzlnfuch,A,SIprockhoirl,Vv i(erxnany; as- 5 A vsignor tb 'Stahlwerk MarkWengernfA'."G;, Wenfgern, Ruhr, Germany, a body corporate of fGer'- manyimputation August 11, 1939,.,seria1`No. .289,619 'x In Germany February.4, 119519` 1 Claim.` (Cl. 121-;26).

rily4 only the advance in the development of the increase in'performance and economy, but in which very heavy recoil 'forces occurwhich soon tire the operator and ,are Ainjnrijmxs to him in continuousWork.

A considerable reduction of the hammer recoil stresses is attainedaccording to the invention in that sudden increases in pressure in thecylinder, such as are produced by the sudden entry of air under highpressure into a space at low pressure, are avoided as the pistoncompresses before the sudden entry of the compressed air the airremaining in the cylinder, so that the compression pressure andcompressed air pressure must be positively the same before the tubularslide valve commences to allow the admission of the compressed air.

For this purpose the slide valve has annular control surfaces and isconstructed as a differential tube, and the position of the outlet apertures is so chosen, that the compression pressure necessary for thereversal is attained after the longest possible compression stroke;moreover thereby that the sizes of the control surfaces on the slideValve are proportioned so that the slide Valve reverses when thecompression pressure corresponds to the actual admission pressure andthat this moment is only reached when the piston has performed its fullstroke, that is, is located as near as possible to the cylinder cover.

An embodiment of the invention is illustrated diagrammatically by way ofexample in the accompanying drawings, in which:

Fig. 1 shows a cylinder in longitudinal section with the slide valveposition during the return stroke of the piston,

Fig. 2 is a similar View, the slide valve being in that position duringthe striking stroke.

According to the invention the tubular slide valve S, axially movable toa limited extent in the cylinder B of the tool, is constructed as asimple differential tube in such a manner that the lower annular endface f1 and the upper end face f3 are constructed as control pressuresurfaces.

valve S and lead to the atmosphere.

As .the outerperphery of the slide valve has an annular enlargement r,another pressure con-V trol surface f2 is formed. The lbore d of thetubular slidevalve S'serves as .gui-de -for the piston k.

The outlet apertures l are arranged in proximity -to the lower end `facef1 of the` slide valve. Theoutlet .apertures aand d are arranged in thewall of the cylinder B- in a position corre'-v sponding -to the outlet`apertures lf in the slide The operation is -as follows: 5

In Fig. l the slide valve vS is in its highest position. The piston .1cis performing its return stroke. Fresh .airflows in .the direction ofthe arrow F into the .fresh air passage g, flows around the tubularslide valve S and passes through the bore h in the wall of the cylinderB into the passage n to the front end m of the piston lc, to force thispiston lc upwards.

The exhaust air A passes into the atmosphere through the bores d and ein the wall of the cylinder B by way of the lower end of the slide valveSV and outlet apertures l in the slide valve with the least resistanceAto movement of the piston lc.

The tubular slide valve S is subjected to the following pressures. Thecontrolling and pressure surfaces f1 and f3 are under atmosphericpressure, whereas the pressure surface f2 is subjected to the fresh airpressure from below, so that the slide valve S is positively held in itshighest position.

Upon upward movement of the piston Ic, the lower outlet bore e is firstclosed with initial resistance oiered to movement of the piston by theholes l and the bore d only remaining open, and when the upper edge ofthe piston o moves over the row of holes l in the slide valve, the eX-haust of air is cut off and the compression commences above the pistonk. The compression pressure bears against the pressure surface f3. Asthe row of holes l in the slide valve S is arranged at the bottom nearthe lower end face, a long compression path is produ-ced with the resultthat the increase in pressure takes place gradually by the successiveclosing of the outlets e and Z-d.

By the construction and arrangement of the slide valve S the surfaceratio of the two effective pressure surfaces f2 and f3 is such, that thecompression pressure must increase to fresh air pressure because f2 isunder fresh air pressure, until balance of the forces is established,and in the case of the slightest increase in pressure,

face o, whereas the lower piston face rm is in' communication with theatmospherefY I A reversing passage c with a lower port Yb leads to thepressure surface j? on the slide vvalve S. As soon as the upper Aedge o;of the piston,

exposes the port b leading tov the reversingl passage c, the cylinderair flows through the revdirectly constructed as a differential tubularslide valve and having a lower end face constructed-as a pres-suresurface, an upper end lface constructed as a pressure surface, a pres-.Y sure' surface formed on the periphery of the versing passage c on tothe pressure face f2 of the slide valve S and again' presses thel slideY valve S into its highest position shown in Fig'. l.

During this movement the exhaust ifair A" below the piston lc isconducted in th'e direction of the arrow into `the atmosphere throughthe passage n, the aperture iin the wall of the cylinder B, around theslide Valve S; through the aperture p into the passage leading to theoutlet aperture d. g By this construction and arrangement of the controlgear the pneumatic percussion tool has extremely weak recoil thrustWithout additionalI auxiliary means,`with thev result that the life ofthe tool is prolonged without reducing its efliciency.

The economy of the tool is very considerably improvedl by thisconstructional measure, because on the one hand the clearance'atthe endof the stroke is already filled with air of the vsame pressure and itsfilling with fresh air is slide `valve adjacent the upper end thereof, apiston reciprocably mounted in the cylinder and slide valve, said slideValve having an annular series of outlet apertures therein below thepressure surface on the periphery of the slide valve, saidlongitudinally spaced outlet apertures in the wall of the cylinder beingspaced below the pressure surface on the periphery of the slide valve,the lower end of the slide valve adapted to form a closure for one ofthe outlet apertures in the cylinder and the wall of the cylinderbetween the outlet apertures therein forming a closure for the outletapertures of the slide Valve when the latter is at its limit'of downwardmovement, the outlet apertures in the wall of the cylinder and in saidslide valve being so arranged that the compression pressure, necessaryfor the reversal and resulting in a considerable reduction in the recoilof the percussion tool, is attained when the piston has performed itsfull stroke in proximity of the cover of the cylinder.

' AUGUST HERZBRUCH.

